Solvent dependence of the visible absorption maxima of meso-tetraphenylporphine

Abstract

Spectral maxima of S 1 and S 2 bands, their vibronic satellites S 11 and S 21 as well as the Soret band have been measured for meso-tetraphenylporphine at room temperature. The increase in polarizability, evaluated from the solvent-induced band shifts in non-polar n-alkanes, is equal to about 5, 15 and 36 Å 3 for S 1, S 2 and the Soret transitions, respectively. The significance of the small and biophysical processes is pointed out. The S 1 and S 2 transition frequencies undergo opposite solvent shifts with increasing dielectric constant. It is proposed that as a result of dielectric screening, the central hydrogen ions move closer to each other. This leads to the reduction of the inequivalence of two NN symmetry axes and to the decrease of S 2−S 1 splitting.